There isn't a gamestop store nearby you? And I think you can actually purchase things online directly from the bestbuy (or gamestop or others) website, don't have to go to the store. Also, even if the games aren't made anymore, according to BCVM, then you still probably can get them "used" in stores. Otherwise I guess Ebay would be a good choice for 4th gen games, just be sure to check the ratings of the seller beforehand to get a good idea whether the person is reliable or not, and that goes for all things you may buy there. Otherwise I don't know if there is an actual way to tell by the description whether the game is real or not. I hope you gave the person who gave you the fake gba game a very bad review/rating.
I'm sorta back
While I'd always love to talk about anything pokemon, I will only be using the 6th gen Wifi section for a while out of efficiency in my life, unfortunately
My 3DS friend code is 0576 3520 6954